The invention relates to photography, and more particularly to photolithography art concerned with photo- and electron-resists.
Known in the art are two types of polymeric photo-electron-resists as follows: positive and negative.
The commercially available positive photo-resists are compositions containing, (a), sulphoethers of 1,2-(2,1)-naphthodiazoquinones, which are the products formed through condensatioon of phenols with formaldehyde, (b), novolac and resol-novolac resins, and, (c), organic solvents such as dioxane and dimethylformamide, with a ratio by weight of about 18:12:80, respectively (cf. F. P. Press, Photolithography for Manufacture of Semiconductor Devices,Energia Publ., Moscow, 1968, p. 40). The positive photo-resists are susceptible to actinic light, including ultraviolet rays, electron beams and X-rays. Their basic property is that they change their physical-chemical properties under the action of the above radiation, with the result that the exposed film becomes more soluble in alkali solutions.
The known negative photo-resists are generally represented by a group having the structure ##STR1## where R is C.sub.6 H.sub.5 and n is an integer from 1 to 5, some particular compositions containing, for example, the derivative of the polyesters of cinnamic, phenylbutadiene- and phenyl-hexatrienecarboxylic acids other unsaturated acids as well as copolymers of vinyl oxycinnamate, .beta.-vinyl oxyethylcinnamate and vinyl acetate and styrene. When such resists are subject to actinic light, cross-linked structures are produced which become less soluble in certain organic solvents (cf. ibid., p.35). The negative photo-resists comprise, in addition to the light-sensitive agents, sensitizers such as Michler ketone, derivatives of anthraquinones and nitro compounds, and organic solvents, for example, toluene, chlorobenzene, derivative, and dioxane. The herein described constituents are employed in a ratio by weight of 3-5:0.3-0.5:94.5-96.5, respectively.
The known photo-resists have a resolution of about 300-500 lines/mm for layer thicknesses from 0.3 to 0.4 .mu.m.
The described photo-resists are disadvantageous in that they yield, during illumination, secondary fluorescence and phosphorescence effects. Since the rays so produced tend to propagate in all directions and possess an energy of about 3 eV, there results a photochemical reaction even at the places covered with the dark field of the mask and the linear dimensions of the components are increased up to 0.15-0.2 .mu.m on each side in the case of positive photo-resists.
The negative photo-resists behave similarly with the exception that an increase in the size of the exposed zone results from a decrease in the non-exposed sections of the resist film, which are washed off during development.
It is known that the resolution provided by light exposure depends on the wavelength of actinic light and generally amounts to 0.3-0.4 .mu.m. This figure represents a theoretically predicted limit for light exposure, which cannot be achieved by the use of the present-day contact method. On the other hand, components of smaller size can be obtained with electron beams. In this case, however, the results achieved in practice are considerably inferior to those provided by theoretical predictions and the smallest sizes of the components after development exceed by the value of the order the diameter of the focused electron beam. The width of the line obtained during the exposure by a movable electron beam of a minimal size will be greater than the beam diameter due to luminescence effect, the scattering of the elecrons impinging on the resist and the reflection of them from the substrate. Note that the line width greatly depends on the thickness of the resist layer. In the case of electron-resists, luminescence is mainly responsible for a distortion of component dimensions, especially for the thickness of resist layers ranging from 0.4 to 1.0 .mu.m. In addition, the stability of photo- and electron-resists is considerably influenced by the side reactions occurring in the solutions and the films based on them. These reactions result in a change of the molecular weight and viscosity, in the formation of cross-linked and degraded structures, and also in the interaction of the resists components and the products of partial degradation thereof with solvents, minute admixtures and atmospheric oxygen. There remains therefore a compelling need for an increase in the resist shelf life, which usually equals about 3-6 months, so as to achieve at least one-year shelf life. Within that period of time, the following properties of resists should be kept invariable: resolution; reproducible image edges; light sensitivity; and stability.